1. Field
This disclosure relates to the field of communications technologies, and in particular to a bias control apparatus and method of a modulator of an optical transmitter and an optical transmitter.
2. Description of the Related Art
In a high-speed optical communications system, it is generally needed to provide a modulator in an optical transmitter to modulate transmitted signals; wherein, in-phase and quadrature (IQ) modulators are widely used in optical communications systems to generate transmitted signals of high spectral efficiencies.
FIG. 1 is a schematic diagram of existing bias control on a modulator of an optical transmitter. As shown by a dotted box in FIG. 1, a modulator 101 of the optical transmitter has two push-pull Mach-Zehnder modulators (MZMs), respectively referred to as a first Mach-Zehnder modulator 102 and a second Mach-Zehnder modulator 103, and a phase modulator (PM) 104, the first Mach-Zehnder modulator 102 and the second Mach-Zehnder modulator 103 being respectively used for modulating driving signals vrf,I and vrf,Q of an I path and a Q path, and the phase modulator 104 introducing a phase difference of 90° between the I path and the Q path. In a normal operating state, the two Mach-Zehnder modulators 102 and 103 and the phase modulator 104 are all biased at respective optimal operating points. However, due to such factors as changes of ambient temperatures, and aging of devices, etc., drifts may possibly occur in all three bias points (denoted by bias I, bias Q, and bias P) of the modulators. Hence, the three bias points may deviate from the optimal operating points.
In order to ensure modulation performance of the modulators, an automatic bias control (ABC) circuit is usually used to respectively track and adjust the three bias points. As shown in FIG. 1, a photo diode (PD) 105 detects output power signals of the modulator 101 of the optical transmitter, and an automatic bias control circuit 106 controls bias voltages VI, VQ and VP on the three bias points, bias I, bias Q, and bias P, of the modulators according to detecting results of the photo diode 105; for example, a method in which pilot perturbation is applied on a bias voltage may be used currently.
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.